I'd say ffmpeg. That`s the tool I would use on my linux desktop and it's downloadable through CLI; root -> apt-get install ffmpeg.

I have not tried the conversion to WAV, but as far as I know ffmpeg supports that. So after installing it your command line option would be something like

ffmpeg -i file.mp3 file.wav

For more info see:

http://howto-pages.org/ffmpeg/